An object of the present invention is to imorove on the efficiency and versatility of operation of pumping systems of the type disclosed in U.S. Pat. No. 4,337,017. Such prior art pumping systems having hoppers for flowable materials which are open to the atmosphere are dependent upon external material filling means and if the hopper is not maintained filled to an adequate level, the pumping system becomes sluggish and inefficient. Also, widely varying consistencies of flowables being pumped are reflected by the changing ability of the dual piston pump to keep up with demand for the pumped material because its operation is affected by changes in material consistency. The dual piston pump can pump with greater efficiency materials of certain thickness and will pump with lesser efficiency materials of different thicknesses.
In accordance with the present invention, the dual alternating piston pump is employed in conjunction with a closed tank hopper in which a substantial partial vacuum is maintained through a vacuum pipe leading from the tank hopper and in communcation with an external vacuum pump. Flowable material from any convenient source is sucked into the tank hopper through a suction line and is pumped out through a material delivery line by the operation of the dual piston pump. Suction created by the dual piston pump is not relied on to fill the tank hopper although it does have a suction boosting effect. Since the evacuated tank hopper can fill itself quickly and maintain a full state during the operation of the dual piston pump, the efficiency of that pump and the overall efficiency of the pumping system is greatly enhanced by the invention.
A further feature of the present invention enables quickly shutting off the vacuum source connected with the tank hopper to allow reversing of the operation of the dual piston pump, whereby material can be drawn into the pump through its delivery line and pumped out through the inlet or suction line. A floating check valve in the rising vacuum pipe prevents material in the tank hopper from being sucked into the vacuum pump and damaging it, and a filter unit connected between the vacuum pipe and vacuum pump further precludes this possibility.
Other features and advantages of the invention will become apparent to those skilled in the art during the course of the following detailed description.